With regard to the background of the present invention, complete inertial nevigation systems have been proposed for use on vehicles, as disclosed for example in U.S. Pat. application Ser. No. 749,356 (now U.S. Pat. No. 4,060,718 which issued Nov. 29, 1977) filed Dec. 10, 1976 and entitled, "Geodetic Survey Method," assigned to the assignee of this invention. In addition, of course, it has previously been proposed to use the odometer of a vehicle and successive compass readings when the vehicle makes turns to track the course of the vehicle.
Considering the second-mentioned system first, it is of course very crude and not easily employed under military field conditions or under other circumstances where accuracy and time constraints are significant factors. With regard to the use of complete inertial navigation systems involving two or three gyros and other associated equipment, such as those employed in commercial aircraft, they are relatively expensive and have a higher cost and greater accuracy than is justified for many applications.
Accordingly, a principal object of the present invention is to provide a simplified low-cost inertial sensor to provide pitch and heading references; and which is capable of rapid initial alignment.
Another object is to provide such a unit which, when used on a wheeled or tracked vehicle in combination with an odometer, will provide both the horizontal and the vertical position of the vehicle, as it travels.